1. Field of the Invention
The present invention generally relates to an antenna device, in particular, to a planar inverted F antenna (PIFA) device applied in a global positioning system (GPS).
2. Description of Related Art
Nowadays, communities of people have growing demands for wireless communication, and various types of wireless communication devices have been developed, including smart phones, multimedia players, PDAs, and satellite navigators using the global positioning system (GPS). Electronic devices provided with the wireless transmission function are improved complying with the design notion of “thin, light, short, and small”, so as to meet the requirements of daily use electronic products.
The conventional GPS antenna applied in the wireless device is usually a chip antenna, a patch antenna, or a planar inverted F antenna. Among them, the chip antenna has a higher price and cost since the manufacturing process of the chip is more complicated than other metal antennas. The patch antenna or the planar inverted F antenna requires a large area, and occupies an effective radiation area on the circuit board, thus greatly lowering the space utilization of the circuit board. In the planar inverted F antenna, the metal radiator thereof is spaced by a suitable distance from the circuit board, and the energy is resonated between the antenna and the circuit board and is radiated in the form of a linearly polarized wave. The architecture of the patch antenna mainly is the chip antenna, and includes a signal feed point, utilizes a ground plane as an energy resonance surface, and radiates in the form of a circularly polarized wave. This antenna has a higher directivity, but requires a larger antenna area and a higher price, and is not applicable to the mobile mode of mobile phones. In addition, the conventional GPS antenna usually contacts the signal feed point or short pad through a pogo-pin or a leaf spring, thus resulting in the difficulties in controlling the resistance.
FIG. 1 shows a structure of a conventional planar inverted F antenna. The planar inverted F antenna 3 includes a planar radiator 31, a feed portion 32, and a ground portion 33. The radiator 31 is disposed above the circuit board 4, and the ground portion 33 extends downwardly from the radiator 31 to electrically connect the ground plane 42 on the circuit board 4 through a ground leaf spring (not shown). And, the feed portion 32 extends downwardly from a position approximately in the middle of the radiator 31 to electrically connect the signal feed point 41. Therefore, in the conventional planar inverted F antenna 3, the signal feed point 41 and the ground plane 42 of the circuit board 4 are not connected.
In the above conventional art, an extending space for the ground portion 33 of the antenna 3 must be provided on the circuit board 4, so as to achieve a better antenna performance. However, under the requirements of improved functions and miniaturization of the hand-held electronic devices, it is difficult to provide extra room for the planar inverted F antenna to ground downwardly. And, as for the GPS antenna, when the planar inverted F antenna is not grounded, even if the size of the radiator is greatly increased, the required frequency cannot be achieved, which not only causes a higher cost, but also goes against the requirements of the miniaturization of the electronic devices.